As a conventional reference electrode, as disclosed in Patent literature 1, there is one that is provided with: an internal electrode formed of a silver/silver chloride electrode; a highly concentrated (1 mol/L or more, including saturation) internal electrolyte solution such as KCl that is in contact with the internal electrode; and a containing body that contains the internal electrolyte solution and has a liquid communication part for bringing the internal electrolyte solution into contact with a sample solution.
However, the conventional reference electrode has a problem that silver ions are eluted from the silver/silver chloride electrode, and by reaction with highly concentrated Cl− ions in the internal liquid, anionic silver complex ions such as silver chloride complexation anions (such as AgCl2−) are produced, and when in the liquid communication part, the silver chloride complexation anions come into contact with the solution having a low chloride ion concentration, at an interface in contact with liquid, silver chloride (AgCl) is reprecipitated to block the liquid communication part, which causes electrode performance to be reduced.
In recent years, in order to solve the above problem, as disclosed in Patent literature 2, an electrode that is, in an internal electrolyte solution, provided with a silver ion adsorbing material that adsorbs silver ions is considered. The electrode is configured such that by adsorbing the silver ions that are eluted on the silver ion adsorbing material, a liquid communication part is not clogged by silver chloride.
However, in a reference electrode having a silver ion trap structure such as the silver ion adsorbing material provided in the internal electrolyte solution as described above, the structure not only complicates a configuration of the reference electrode but becomes a factor for causing the reference electrode to be enlarged or preventing the reference electrode from being downsized. Also, the reference electrode having the silver ion trap structure as described has a problem because the reference electrode is invented from the perspective of preventing the silver ions eluted from a silver/silver chloride electrode from flowing outside, and when efficacy of the silver ion trap structure is reduced, the liquid communication part is clogged by silver chloride after all unless the internal electrolyte solution is regularly replaced, which necessitates the replacement of the reference electrode itself.